LAST EDITED ON 24-Oct-01 AT 07:43 AM (PST)

There was a discussion on this over at ASOG, but I thought it was worthwhile over here to make the same post since there are so many turbo'ed peeps.

I had a probem about a month ago with my air-fuel ratio as I was mysteriously going lean at WOT. After a few calls with Bill Hahn and doing a bunch of sensor checks, buying a new fuel rail with injectors, a new map sensor, changing fuel filters, new spark plug wires, and two sets of spark plugs, I FINALLY found out what caused my leanness. My HRC fuel mapper(or FCD) was clamping my voltage at 3.3-3.5 volts thereby sending an extremely low map sensor voltage to the ecu and it in turn sending a low voltage to my fuel injectors. The HRC fuel mapper apparently worked properly for over a year, but for some reason failed me as of late. HRC was happy to take it back, bench test it, and send me a new one. The new one clamps at about 4.35-4.5 volts. I'm not sure I'm happy with this voltage clamp level, so I've looked into alternatives.

I've seen what some other turbo owners use, and many either go by way of HKS fuel cut defensers or what's called a Zenier Diode. Both of these items also clamp your map sensor/MAS sensor voltage so your car won't freak out upon seeing too much boost (or any boost in our cars). The Zenier Diodes go for about .10-.20 cents while the HKS FCD's are about $70 and up.

The thing is now, I want a voltage clamp that will not only be reliable, but not fluctuate every time I start the car, much less as an ordinary side effect of its operation.

Split Sec is of course the company that supplies the VC-1 to individuals who run the STAR turbosystem. After a conversation with those folks, they told me that their product, the VC-1 clamps the voltage at 4.75-4.85, but it was a "soft clamp," so again, fluctuation would be a normal by-product of its operation. They did tell me, and I've heard from a second source, that a VC-2 was coming out very shortly (possibly within a month) that would be a "hard clamp" and not fluctuate and also be adjustable.

That sounds most appealing to me, so I can set the voltage clamp myself, and hopefully find the highest level of voltage my car will allow, before freaking out. I'm just wondering what level of map sensor voltage activates the injectors to operate at maximum fuel cycle. (I'm also wondering if the Spli Sec product may be more reliable since it has its own 12v power feed and ground as opposed to the more simply installed HRC fuel mapper that merely takes the output Map sensor voltage and its ground.)

I just don't want a large amount of fluctuation that will effect the tuning of my car everytime out. Am I supposed to build in a large amount of safety for a fluctuatiing voltage clamp? Am I supposed to tune my S-AFC every time I get in my car to account for a fluctuating voltage clamp?

Just seems important to me if people out there have disfunctional voltage clamps that could or might cause a dangerous amount of leanness in your car. Do your "check sensors" on your S-AFC screen at WOT and see what voltage you get. I'm sure many (or most) are fine...but if not, watch out for leanness caused by a fluctuating or failing voltage clamp.

Jason
98' Eagle Talon ESi-T
Mitsu Super 16g Turbo(HRC)/Custom FMIC

http://springfielddsm.homestead.com/JasonsPics.html

Thanks for the heads up Jason. Since day one, I have always wondered about the reliabilities of the VC-1 that I use. During my install just out of curiosity I opened the VC-1 and found how simple it was....just resistors and and such. Something you could make at RadioShack:) The VC-2 sounds like a much better product.

When you say its "hard clamped" is that reffering to how its connected to the map? I have mine soldered so in my thinking just using butt connectors would be "soft clamped"????




chris
blitzdsm1@aol.com

>When you say its "hard clamped"
>is that reffering to how
>its connected to the map?

No, from my conversation with the Split Sec people, it's a techno-term referring to the fluctuation that's "expected" with a "soft clamp."


Jason
98' Eagle Talon ESi-T
Mitsu Super 16g Turbo(HRC)/Custom FMIC

http://springfielddsm.homestead.com/JasonsPics.html

LAST EDITED ON 24-Oct-01 AT 12:19 PM (PST)

Turbos are gay, everyone should just buy a camaro.

The SplitSec VC-1 for us clamps at 4.7v.. This equates to WOT, atmospheric, NA operation; zero pressure, zero vaccuum. The VC-1 only clamps when the voltage it sees (the map sensor output) moves to 4.7v, at which point the VC1 supplies 4.7v to the ECU, totally ignoring whatever the map sensor is outputting until it moves below 4.7v (this is why it has a 12v power and ground, why it needs an external source of power) .. From what i understand, the HRC fuel mapper has no external source of power and uses the circuitry in itself to limit the voltage supplied in boosted operation to acceptable limits (which i think would be higher than 4.3 something volts) .. i can't see it as being 100% reliable. My opinion would be to talk to Wyatt, and buy a VC-1. From what i've seen on cars that use them in conjunction with an SAFC displaying a pressure reading, hit boost and the SAFC will peg at +.01 mB and sit there. Zero fluctuation.

_____________________________________________
-Dino Yancey
Hello me, it's Me Again!




For Mitsubishi Technical Manuals, INCLUDING the 97-99 electrical and service manuals, click HERE:
http://www.heavenz-not-0verflowing.com/files/
No MP3 for YOU!

Yeah Dino...

After thinking about the HRC Fuel mapper as opposed to the VC-1, I would agree with your assessment of the importance of an external source of power.

Jason
98' Eagle Talon ESi-T
Mitsu Super 16g Turbo(HRC)/Custom FMIC

http://springfielddsm.homestead.com/JasonsPics.html

In addition to your comments, I would like to add that as far as the avenger/sebrings with the OBD-II systems and 420a I4 engines, the maximum voltage the map sensor can see before the ECU freaks out and fuel cuts at 4k rpm is 4.79V. Its listed in the service manual. And I know for a fact that's the voltage because my map sensor went bad and hit the 4.79V reading and my idle was crap and fuel cut at 4k rpm.

So I would assume that anyone planning to use a VC-2 and that wants to get the max voltage and fuel injector rating should set their VC-2 as close as possible to 4.79V but NOT at 4.79V. Perhaps at 4.70V would get you the max fuel without going into ECU-limp mode.

Price of the VC-2 is estimated to be around the same of the VC-1, maybe a few dollars more. I believe they mentioned to me 80 bucks or so.

Vinnie
aka Kiku
www.asog.net

Jason
98' Eagle Talon ESi-T
Mitsu Super 16g Turbo(HRC)/Custom FMIC

http://springfielddsm.homestead.com/JasonsPics.html

Dino wat are u talking about????



Kory
fasteclipse@cisco.com
aim sn: dukmahsik
Happy Honda Hunting!

I have a feeling someone just got on Dino's cpu and did a little sabotage job...

Not like Dino to like Camaro's all of the sudden. (heh)

Jason
98' Eagle Talon ESi-T
Mitsu Super 16g Turbo(HRC)/Custom FMIC

http://springfielddsm.homestead.com/JasonsPics.html

HMM.... There's only one guy i know that drives a Camaro (besides tha one i know who totaled his) who knows me well enough to know.. hmm..

Ryan, i'm gonna come and make that 5.7 feel like a Hondah in about 2000 miles.

_____________________________________________
-Dino Yancey
Hello me, it's Me Again!


For Mitsubishi Technical Manuals, INCLUDING the 97-99 electrical and service manuals, click HERE:
http://www.heavenz-not-0verflowing.com/files/
No MP3 for YOU!

I hate to bring up this company but JET has an adjustable universal fuel ut denfenser but I'm not sure of the range of adjustability (and I'm glad to have a 95' although I wonder if I get any "unoticeable" ill effects from the extra voltage).


http://stan2gnt.homestead.com/home.html
Stan2gnt
Stan2va@aol.com
95 Talon 420A-Turbo
Former and future nitrous user